What's the best string quartet written by an American?

I was thinking Ruth Crawford-Seeger when I read the thread title, I envy you getting to see a performance

George Crumb "Black Angels"
Ben Johnston "Quartet No.2" & "Quartet No. 4 (Amazing Grace)"
Philip Glass - "Quartet No. 3 (Mishima)"
John Cage - "Quartets I-VIII" (this is cheating, as it's a piece for large ensemble, though only four people are allowed to play at any one moment. it's beautiful & one of his rare late tonal pieces, all the materials are sourced from early American church hymnals and then pulled and stretched into shifting ambient blurs)

I like Ives' two quartets but not as much as his "Trio"

i like this one!

http://www.musicroom.com/images/catalogue/productpage/GS34173.jpg

i like most the stuff milton named too. except i don't think i know who ben johnston is.

studied & performed with Harry Partch, wrote in just intonation. very religious about microtonality, there's an interview where he attributes aspects of western illnesses to our listening to music in equal temperament (though I say 'screes' I think there is definitely something to what he's saying)

'Microtonal Piano' performed by Philip Bush is my favorite album of his music, these are the two for the quartets:

http://www.discogs.com/release/772028
http://www.newworldrecords.org/album.cgi?rm=view&album_id=15254

gershwin "lullaby" for str qt is maybe my fave gershwin

I don't know what's the best but Lejaren Hiller's 5th (in Quarter Tones) is great and could use a shout-out. I really like the modest open-form compositional ideas in Earle Brown's although the recording I have of it (Concord) doesn't stand out as a mind-blowing piece. Still good though. I'd like to hear the Johnston. I love Microtonal Piano.

I should listen to the Cage again. I remember liking it.

the recording I have of it (Concord) doesn't stand out as a mind-blowing piece.

I was wrong. It's totally intense. I might even nominate it.

The Cage is lovely, of course.

Mmmm! I just got a Naxos CD of Carters #1 and #5, and enjoyed both. #1 was the crowd pleaser, with lots of beautiful long notes swelling up under quick pizzicatos and bowed notes; #5 was weird and disjointed, but it's got personality. But yeah, Crumb or one of the Glass may be better--though I don't think Glass #3 is the one I like the most. I'd have to find the CD. That Cage is OK, but for static long note stuff, not as compelling as what I've heard of Feldman.

Some more stuff worth hearing:

Mel Powell, String Quartet 1982 -- the more modest Filligree Setting (1959) and the Little Companion Pieces (1979) are lovely as well, although the latter isn't really a string quartet, since it follows the model of Schoenberg's Second String Quartet and adds a soprano voice.

Stefan Wolpe, String Quartet (1969)

Roger Reynolds, Coconino -- also Ariadne's Thread, which adds digital audio.

Andrew Imbrie, String Quartet No. 4 (1987)

Charles Wuorinen, Third String Quartet (1987)

And out of all the Babbitt quartets I've heard, the Second (1954) is my favorite.

pedantic correction: the 1987 Imbrie quartet is his 5th, I'm less keen on the 4th